The open hatch leading to Zarya module. Photo: NASA-JSC

The astronauts will float into the space station the day after the spacewalk - flight day five - to begin transferring supplies and equipment into the outpost. The goal is to outfit and activate the Zvezda module, which will provide the station's initial crew quarters and the propulsion needed to maintain a safe orbit.

Running two years behind schedule because of Russian funding shortfalls and recent problems with Proton boosters, Zvezda was finally boosted into space July 12, clearing the way for arrival of the lab's first full-time crew in November.

To save weight, Zvezda was launched with just five of its eight batteries installed and with many of its modular life support and control systems incomplete.

Some of the missing equipment, along with crew supplies, food and other material, was launched Aug. 6 aboard the Progress 251 vehicle now docked to the far end of Zvezda. Additional equipment and supplies will be launched aboard Atlantis in a double Spacehab module mounted in the shuttle's cargo bay.

The astronauts will be hard pressed to completely unload both vehicles during the five days Atlantis is docked to the station.

"There are over 600 kilograms of cargo in the Progress cargo hold," Morukov said. "We made an attempt to load the cargo in the sequence that would best fit the unloading process and the accommodation aboard the station.

"Some of the cargoes are packed in U.S.-made bags that are very easy to accommodate on the station and which have specified preset locations," he added. "Other cargos - large components in boxes for the various systems - will be installed into the locations where they will be operated subsequently. This cargo complement includes very important components of the life support system.

Illustration of the Progress freighter docked to the end of Zvezda. Photo: NASA TV/Spaceflight Now

"Probably the most important objective of the Progress flight is to deliver propellant to the station. However, the crew is not involved in the propellant transfer."

The Atlantis astronauts will, however, use spare fuel aboard the space shuttle to boost the station's altitude by about three nautical miles (six kilometers), saving the station's propellant for use when the shuttle is not available.

Morukov is responsible for orchestrating the Progress unloading. Burbank will direct stowage and assembly operations in the space station while Mastracchio will organize the unloading of the Spacehab module.

"Not only are we taking cargo and logistics from the orbiter but we're also bringing them across the hatch from the Progress into the service module," Burbank said. "It's going to be a major exercise in choreography. The key to all that is just doing the homework ahead of time."

Along with moving supplies into the station, the astronauts will assemble a Russian Elektron oxygen generator, a carbon dioxide removal system and major components of the station's toilet. They will also assemble a NASA-supplied treadmill and install laptop computers and equipment to set up a local area network.

Two new batteries will be installed in the Zarya module - four were replaced during the most recent shuttle visit in May - and three batteries and their charge-discharge controllers will be installed aboard Zvezda, giving the module a full complement of eight.

Astronaut Ellen Ochoa transfers supplies from the Spacehab module during a space station docking mission in 1999. Photo: NASA-JSC

All told, Atlantis will carry 4,817 pounds (2,186 kilograms) of gear that will be transferred to the station, including 722 pounds (327 kilograms) of Russian hardware, 858 pounds of food (389 kilograms), 784 pounds (356 kilograms) of fresh water generated by the shuttle and 1,150 pounds (522 kilograms) of exercise equipment.

The Progress 251 vehicle is loaded with some 1,313 pounds (588 kilograms) of material, including components for the Elektron oxygen generator, the carbon dioxide air scrubber and toilet components.

"One of the primary goals of STS-106 is to get that vehicle off loaded because we will need an additional vehicle, Progress 2, to deliver the remaining supplies that are required to meet the early initial conditions for the crew, to have all the necessary supplies," Engelauf said.

"In addition, we will be off-loading a significant amount of cargo from the Spacehab," he said. "After we arrive, we'll move some of the supplies from the Zarya into Zvezda, we'll unload some equipment out of the Zarya that is no longer required. ... In addition, we'll be transferring a couple of science payloads."

Other objectives include:

• Installation of new software into computers in the Unity module to help control the P6 solar array when it arrives later this year
• Measurements of air quality in the station and the background acoustic environment
• Installation of air ducts and fans in Zvezda
• Removal of no-longer-needed manual docking control equipment in the Zarya module to make room for other equipment
• Installation of U.S.-to-Russian power converter units to enable Russian equipment to use power generated by the P6 solar array
• Installation of a bar code reader system to track station inventory and stowage locations
• Removal of launch restraint bolts from fire extinguishers in the Zvezda module
• Removal of Zarya's aft docking probe, which is no longer needed

The station's first full-time crew - commander William Shepherd, Yuri Gidzenko and Sergei Krikalev - will complete activation of Zvezda's life support systems after arrival in early November.

"We've basically got a house up there that we're trying to get ready for somebody else to move into but half the systems aren't installed," Lu said.

"We're going to show up with two big moving vans - a shuttle and a Progress - and we've got five days once we get up there for all of us to unload all that stuff, get it put together, install it in its proper place and ... get a lot of systems up and running or ready for the Expedition One crew to do that themselves."

Because of the sheer volume of material to be transferred, stored and set up in the station, NASA managers are holding open the option of extending Atlantis's mission by one day.

"It's very aggressive and our list of things that we can do productively on this flight exceeds the amount of time we're going to have available," Engelauf said.

But a decision to extend the flight likely will not be made until after the shuttle is in orbit, based on the shuttle's actual power consumption. If the flight is not extended, Atlantis will undock from the station late in the evening (Eastern time) on Sept. 16.

The space station is photographed over Mongolia just after separation from the Atlantis' last mission in May. Photo: NASA-JSC

"We'll put the vehicle in the same orientation as when we docked, with the orbiter out on the radial outward side from the Earth relative to the stack," Engelauf said.

"We'll separate away to a distance of about 450 feet from the center of gravity of the vehicle and the crew will initiate a fly around. This is going to be our first opportunity to do a good exterior inspection of the Zvezda since we arrived on orbit."

Over the next two days, the astronauts will relax and enjoy a bit of time off before testing re-entry systems and gearing up for a pre-dawn landing at the Kennedy Space Center on Sept. 19.

"This is a tremendously important mission," Altman said. "We're preparing the international space station for its first occupants. So I feel a heavy responsibility as far as putting things together, making sure everything is up and ready for them when they arrive, so that they can get right to work without having to deal with any of the hassles of basically building a new house. We want to have it ready for move-in when we're complete."